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Updated: May 31, 2025
The arenaceous laminae are much hardened at the point of contact, and the clays are converted into siliceous schist. In this island the altered rocks assume a honey-comb structure on their weathered surface, singularly contrasted with the smooth and even outline which the same beds present in their usual soft and yielding state.
The range in the Crimea from Cape Kersonese to the Bay of Ratla is formed of layers of limestone alternating with clay and argilaceous schist, a disposition of the strata that tends greatly to accelerate the disintegration of the cliffs. The clay gradually washed out by springs or eaten away by the weather forms great caverns in the sides, and these are liable to fall in when deprived of support.
At last we observed near the catacombs sundry heaps of pinkish earth, evidently washed out; and our researches in the South Country afterwards suggested that this may have been the remains of the micaceous schist, whose containing quartz was so extensively worked at Umm el-Harab. Moreover, a short study of Shaghab threw more light on the matter.
We began our descent into this great valley when we left the source of the Bua; and now these low hills, called Ngalé or Ngaloa, though only 100 feet or so above the level we had left, showed that we had come to the shore of an ancient lake, which probably was let off when the rent of Kebra-basa on the Zambesi was made, for we found immense banks of well-rounded shingle above or, rather, they may be called mounds of shingle all of hard silicious schist with a few pieces of fossil-wood among them.
We have Mr. Bruce's word for these mouldering shells, and we have the absolute certainty that such decomposing shells could not be incised by a hand of to-day, as shale, slate, schist, and sandstone can now be engraved upon, fraudulently.
He spoke no Hindoostanee, but was very communicative through my interpreters. Leaving the Lingcham spur, we passed steep cliffs of mica and schist, covered with brushwood and long grass, about 1000 feet above which the Changachelling convent is perched.
Now it is most fortunate for natural history, that it has been in this range of mountains that we have discovered those marks of a marine origin; for, I shall afterwards have occasion to give the clearest light into this subject, from observations made in other parts of those same mountains of schist, by which it will be proved that they are the primary strata; and thus no manner of doubt will then remain in the minds of naturalists, who might otherwise suspect that we were deceiving ourselves, by mistaking the secondary for the primitive schistus.
It added the human touch of melancholy to the sadness of the picture. More and more gloomy became the scene. Great black precipitous rocks of schist, their hollows filled with sombre foliage, rose in solemn grandeur far above me, and in the bottom the plunging stream foamed and roared. The mad wind caught up the dust from the road and whirled it onward, and then the rain began to fall.
The mica schist almost always dipped toward the interior of the country, forming those mountain ranges of which we have already spoken as giving a highland character to the district of Golungo Alto. The trap has frequently run through the gorges made in the upheaved rocks, and at the points of junction between the igneous and older rocks there are large quantities of strongly magnetic iron ore.
I have already hinted at the close analogy in the forms of certain granitic and trappean veins; and it will be found that strata penetrated by Plutonic rocks have suffered changes very similar to those exhibited near the contact of volcanic dikes. Thus, in Glen Tilt, in Scotland, alternating strata of limestone and argillaceous schist come in contact with a mass of granite.
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